The invention is directed to an extrudable compound, an extrusion method using primarily waste polyolefin starting materials, and articles manufactured through such processes which simulate conventional outdoor construction lumber.
There are many advantages to recycling waste plastics both economical and ecological. Discarded waste plastics are available at comparatively negligible costs since they are essentially garbage. Furthermore, the present invention provides an economic incentive to remove waste plastics, which ordinarily are not completely bio-degradable, from the environment.
Waste polyolefins and other waste plastics are different from plastics fresh off a plastic manufacturer's production line because these materials have served their intended use, been discarded and exposed, often for lengthy periods, to the environment. This relatively lengthy exposure to the elements produces changes in the physical and chemical properties of the plastics. Generally, waste plastics have lower tensile strength and relatively poorer flex and thermal properties when compared to new plastics fresh off the production line.
Since waste polyolefins are not completely biodegradable, they have life cycles which are much longer than conventional wooden building materials. In addition, construction materials made from waste polyolefins have chemical, biological, mechanical, electrical and fame resistance properties superior to counterpart natural lumber products.
Surprisingly, only limited attempts have been made to develop lumber-substitute construction products from waste polyolefins. For example, U.S. Pat. No. 4,003,866 teaches construction material made from waste thermoplastic resins and other non-plastic fillers. The non-plastic fillers are coated or encapsulated with a recycled polyethylene or polypropylene wax. Because of the complexity of the process disclosed and the limited improvement provided by the wax encapsulated materials over natural materials, the products made from this disclosure have very narrow practical application.
Maczko, J., A System to Mold Mixed, Contaminated Plastics into Wood, Metal and Concrete Replacements, RECYCLING-PLAS II, Conference of Plastics Institute of America, Jun. 18-19, 1987, Washington, D.C., describes the ET-1 process for producing substitute construction materials from waste plastics. The described method is claimed to be able to transform mass waste plastics directly into a large range of molded end products without presorting of any kind, and without the need for inserting any additives to the intermediate resin.
The ET-1 process melts resins in a short-screw extruder, then forces the heated extrudate into a series of linear molds which are then mounted onto a turret. The heated molds cool as the turret rotates them through a water filled tank. The end products are air-ejected from open ends of the molds.
The ET-1 end product is essentially a solid with randomly spaced voids. It has a typical specific gravity slightly higher than 1.0 gm/cc, making it heavier than most natural timber products (ordinarily, wood floats on water because it has a density less than that of water). The length of the end products are limited by the size of the mold into which the extruder can inject and fill with resin. Practically, as construction material, these end products are generally difficult to cut, saw, nail or drill holes into.
Accordingly, there is a need for a recycled waste plastic material which has qualities closely resembling natural lumber such as consistency, texture and density which will be readily accepted by the construction industry as a replacement for wood. Such materials can be used by architects, construction engineers and manual construction laborers by applying heir currently known skills to the use of such recycled waste plastic products.
Known extrusion methods have not been able to satisfactorily convert waste plastics into products that have uniform dimension due to variations in the feed composition, and the end products produced, undesirably and unpredictably, vary in size, configuration and thickness. The need therefore exists for an extrusion process which produces end products derived from waste plastics with substantially uniform dimensions conforming to conventional construction standards of any desired length.